Federal investigators said they watched Kenneth Trapp for more than a month before they busted him on the way home from an out-of-state shopping spree that allegedly included new underwear, boots and 1,200 bags of heroin.

The Castleton man was arrested Tuesday afternoon when Vermont State Police stopped the taxi he was riding in soon after it crossed the New York border into Vermont on Route 4.

State police Lt. Charles Cacciatore said Wednesday that police stopped the taxi for speeding. But an affidavit filed in U.S. District Court Wednesday afternoon made it clear that police and U.S. Drug Enforcement Administration agents expected to find more than just bags of merchandise when they stopped Trapp on his way home from a trip to Lake George, N.Y.

Trapp, 31, came to the attention of federal and state drug investigators a month ago when New York State Police said they found $1,499 in cash and a small amount of marijuana on him during a traffic stop.

DEA Agent Thomas Doud, who wrote the affidavit, said police in New York seized that money “relative to their belief that it related to the distribution of narcotics.”

The incident in New York led state police there to contact the DEA, which in turn called Rutland City Police who said an informant had previously told them that Trapp was making daily trips to Rutland to deliver heroin to dealers here.

On Tuesday, Doud said an informant told federal agents that Trapp would be traveling by taxi from his Route 4A home to the outlet stores in Lake George to buy heroin.

Federal agents contacted New York State Police, who reported they watched Trapp travel from store to store with a black plastic bag.

At the Ralph Lauren Polo store, police said, they saw Trapp meet a woman and leave the store without the plastic bag.

Doud said the woman was Danielle Goding, of Brooklyn, N.Y., who was stopped in a rented Lincoln Continental bound for New York City. In a Louis Vuitton box in the back seat, police said, they found $13,800 in cash.

Police said Goding told them the money was from insurance proceeds and she was going to use it while shopping in Florida.

In a subsequent interview with Doud and other investigators, Goding allegedly told police she had met Trapp about three times in the past and suspected he was involved with the distribution of drugs but denied giving him any.

Asked by investigators why she would not “admit that she was involved in transporting drugs,” Goding allegedly said she was afraid of being killed.

While police in New York arrested Goding, Vermont State Police were waiting at the border when Trapp returned to the state, Doud wrote.

After obtaining a warrant to search the taxi — and with the help of a state police dog — police said they found 1,200 bags of heroin hidden inside a new pair of underwear and boots.

Trapp was arrested and taken to state police barracks in Rutland, where Doud said he had little to say to investigators other than that he followed phone instructions from a man known to him as “TK.”

Trapp and Goding have both been charged with a single federal charge of conspiracy to distribute heroin.

Goding was freed on court-ordered conditions. But Trapp, who federal prosecutors said in court records has admitted that he is not a U.S. citizen, remains in the custody of the U.S. Marshals Service pending a detention hearing Monday.